Froth flotation is a well known metallurgical technique for beneficiating various mineral ores and separating their components for subsequent recovery or disposal. An aqueous pulp is inundated with gas bubbles. By judicious additions of frothers and surfactants, the hydrophobic and hydrophilic natures of the particles comprising the pulp are enhanced to effect separation. Normally, a fraction of the conditioned pulp with hydrophobic particles will tend to float. These particles may be skimmed off the top and routed for subsequent processing. Similarly, the hydrophilic particles tend to remain in the pulp. These latter particles can then be discharged for subsequent processing.
Of the various froth flotation systems currently in use, column flotation tends to give superior metallurgical results, particularly, better concentrate grade due to the wash water addition at the top of column. A gas, usually air, is introduced through spargers at the bottom of the column to generate bubbles therein.
Particle collection by bubbles in a conventional flotation column is considered to occur by bubble/particle encounter mechanisms in which hydrophobic particles collide with and subsequently attach to bubbles. Particles attached to bubbles will rise to the column top and will overflow as concentrate. The hydropholic particles that collide with but do not adhere to the bubbles will descend to the column bottom and be discharged as tailings. Some flotation column designs utilize mechanical mixers disposed in the column to effect separation. However, to optimize the flotation process in columns, the bubbles must flow at a minimum flow velocity since relatively quiescent conditions are required.
The success in column flotation has led to many new developments. Among these new developments, the Jameson.TM. cell and the Microcel.TM. column are considered to be superior than the conventional columns. There is a common point in these two types of columns: pulp aeration before entering column. In the Microcel column, air is introduced using an in-line static mixer. This eliminates the problems inherently associated with the conventional internal air spargers. The column itself is identical to the conventional column: 10-12 m in length and 1-2 m froth zone. In the Jameson cell, air is aspirated into a pipe called a downcomer using a high-velocity feed slurry jet at the top. There are some problems with the aeration device in the Jameson cell. Finally, the work at the U.S. Bureau of Mines shows that direct contacting between newly formed bubbles and particles improved flotation kinetics by as much as 10 times compared to aged bubbles.